1. Field of the Invention
The present invention relates to an alternator, and particularly to a stator for an alternator mounted to an automobile, etc., enabling reductions in size and increased output, and to a method for the manufacture thereof.
2. Description of the Related Art
A conventional stator for an alternator is prepared by installing conductor wires having a circular cross section in slots of a stator core, then pressing the conductor wires housed inside the slots in a slot depth direction, and then making the slot openings half-open by flaring the tips of the tooth portions of the stator core to first and second circumferential sides.
However, one problem has been that improvements in the output of the alternator cannot be achieved when conductor wires having a circular cross section are housed inside the slots because the space factor (the ratio occupied by the conductor wires in the slots) cannot be improved due to space inevitably arising between the conductor wires.
When conductor wires having a circular cross section are installed in the slots, the conductor wires cross each other inside the slots, and the conductor wires are not housed in an aligned state inside the slots. If conductor wires housed in this state are pressed in a slot depth direction, an electrically-insulating coating on the surface of the conductor wires is damaged, giving rise to short-circuiting among the conductor wires. As a result, another problem has been that the rate of production of the stator declines.
In order to solve problems of this kind, a stator for an alternator is proposed in Japanese Patent Non-Examined Laid-Open No. SHO 63-194543, for example, which is prepared by preparing winding portions by winding conductor wires having a circular cross section for a predetermined number of winds, press forming portions of the conductor wires of these winding portions to be housed in the slots into a quadrangular cross section, and then installing the winding portions in the stator core such that the portions of the conductor wires formed with the quadrangular cross section are inserted into the slots.
FIG. 23 is a partial cross section showing a conventional stator for an alternator described in Japanese Patent Non-Examined Laid-Open No. SHO 63-194543, for example, FIGS. 24 to 26 are all diagrams explaining a method for forming a stator winding in the conventional stator for an alternator, FIG. 27 is a perspective showing part of a stator core before installation of the stator winding in the conventional stator for an alternator, and FIGS. 28A and 28B are diagrams explaining a method for forming flange portions of the stator core in the conventional stator for an alternator.
A conventional stator 1 for an alternator, as shown in FIG. 23, includes: a stator core 2; and a stator winding 4 installed in the stator core 2.
The stator core 2 is prepared by laminating a predetermined number of steel sheets punched into a predetermined shape, being constructed such that tooth portions 7 disposed so as to extend radially inward from an annular core back portion 6 are arranged at a predetermined pitch in a circumferential direction. Slots 3 are defined between adjacent pairs of the tooth portions 7. Flange portions 5 are formed on tip portions of each of the tooth portions 7 so as to project toward first and second circumferential sides. These flange portions 5 serve a function of collecting magnetic flux, and also serve a function of preventing popping out of the stator winding 4 by closing approximately half a width of the openings of the slots 3.
The stator winding 4 is installed in the stator core 2 such that three-phase output can be obtained. In each of the slots 3, as described below, slot-housed portions 12a formed by press-deforming a portion of conductor wires 11 having a circular cross section into a rectangular cross section are housed so as to line up in single rows in a radial direction.
Furthermore, insulators 8 having high heat-tolerance are mounted into each of the slots 3, ensuring electrical insulation between the stator core 2 and the stator winding 4.
A method for forming the stator winding 4 will now be explained.
First, as shown in FIG. 24, a lap winding 10 having a plurality of rectangular winding portions 12 is prepared by forming a first rectangular winding portion 12 by winding one conductor wire 11 having a circular cross section into a substantially rectangular shape for a predetermined number of winds (six winds, for example), and then winding the conductor wire 11 projecting from this rectangular winding portion 12 for a predetermined number of winds so as to form a second rectangular winding portion 12, and so on.
Next, each of the rectangular winding portions 12 of the lap winding 10 are mounted onto a press forming machine 13, as shown in FIG. 25. Here, the slot-housed portions 12a are superposed in single rows and inserted between a stopper 15 and slides 14 slidably supported by springs 16. Then, the slot-housed portions 12a are pressed in the direction of the arrow by a pusher 17. Hence, as shown in FIG. 26, the slot-housed portions 12a of the lap winding 10 are formed with a rectangular cross section. Moreover, coil end portions 12b linking the slot-housed portions 12a have a circular cross section.
The slot-housed portions 12a of the lap winding 10 constructed in this manner are inserted from an inner circumferential side into each of the slots 3 of the stator core 2 shown in FIG. 27. Here, the lap winding 10 is installed in the stator core 2 by inserting the slot-housed portions 12a into every third slot 3. As shown in FIG. 28A, the insulators 8 are mounted in each of the slots 3 and the slot-housed portions 12a are housed in six layers so as to line up in single rows in a radial direction. The stator winding 4 is constructed by installing three lap windings 10 in the stator core 2 such that the slots 3 into which the slot-housed portions 12a of each lap winding 10 are inserted are offset by one slot each.
Next, tip surfaces of the tooth portions 7 of the stator core 2 are pressed by a roller, etc., (not shown) in directions indicated by the arrows F in FIG. 28B. Hence, penetrating apertures 9 formed on the tip portions of the tooth portions 7 are crushed, and portions on first and second circumferential sides of the penetrating apertures 9 are pushed circumferentially outward, forming the flange portions 5.
In this conventional stator 1, the slot-housed portions 12a having a rectangular cross section are housed in six layers in each of the slots 3 so as to line up in single rows in a radial direction. Bundles of six coil end portions 12b of each of the lap windings 10 leading out from any given slot 3 and leading into the next slot 3 three slots away in a first circumferential direction are each arranged at a pitch of six slots in a circumferential direction, constituting coil end groups. In these coil end groups, the maximum radial overlap of the bundles of coil end portions 12b is three bundles.
In the conventional stator 1 constructed in this manner, because the slot-housed portions 12a of the lap winding 10 are formed with a rectangular cross section before being inserted into the slots 3, gaps are less likely to arise between the slot-housed portions 12a housed inside the slots 3. As a result, the space factor is improved, enabling improvements in the output of the alternator.
Because the press forming machine 13 is used to press deform the slot-housed portions 12a of the rectangular winding portions 12 of the lap winding 10 into a rectangular cross section after forming the lap winding 10 using one conductor wire 11, the slot-housed portions 12a can be set between the slides 14 and the stopper 15 in an aligned state, enabling the occurrence of damage to the electrically-insulating coating of the conductor wires 11 resulting from press deformation to be suppressed. As a result, the occurrence of short-circuiting among the conductor wires 11 is suppressed, enabling reductions in the rate of production of the stator 1 to be prevented.
Because the coil end portions 12b have a circular cross section, the occurrence of damage to the electrically-insulating coating resulting from rubbing among the coil end portions 12b is suppressed, improving electrical insulation.
Because the conventional stator 1 for an alternator is constructed by installing three lap windings 10 in the stator core 2 such that the slots 3 into which the slot-housed portions 12a of each lap winding 10 are inserted are offset by one slot each, a maximum of three bundles of six coil end portions 12b overlap in a radial direction at the axial ends of the stator core 2. Thus, large bending stresses resulting from contact between the bundles of coil end portions 12b act on the coil end portions 12b. These bending stresses are concentrated at the boundary between the slot-housed portions 12a and the coil end portions 12b and one problem has been that the electrically-insulating coating at the boundary is damaged, giving rise to incidents of short-circuiting among the conductor wires 11.
In the method for manufacturing the conventional stator 1 for an alternator, because the slot-housed portions 12a of the lap winding 10 are inserted into each of the slots 3 of the stator core 2 from an inner circumferential side and then the flange portions 5 projecting from the first and second circumferential sides are formed by pressing the tip surfaces of the tooth portions 7 from an inner circumferential side and plastically deforming the tip portions of the tooth portions 7, irregularities arise in the shape of the flange portions 5. As a result, another problem has been that when the stator 1 is mounted to an alternator, the magnetic circuit becomes unbalanced, leading to aggravation of electromagnetic noise.